The process for making bends in said pipes, characterized by radius and angle, implements tools which normally include a forming roller that rotates around an axis orthogonal to the initial direction of the pipe to be bent, having an annular groove on its periphery and supporting, or forming in and of itself, a first clamping jaw, with a second clamping jaw held by a bending arm mounted to turn around the axis of the forming roller, said second clamping jaw moving on said arm and cooperating with the first clamping jaw in order to hold and pull the pipe to be bent, with a strip parallel to the initial direction of the pipe being placed behind the clamping jaw, designed to be applied laterally against the pipe to be bent.
In this way, in order to form a bend in a section of the pipe to be bent, said section is clamped between the two clamping jaws and moved forward by the rotation control of the bending arm, so as to wind into the groove of the forming roller, while the strip, applied laterally against the pipe behind the section being bent, prevents any undesirable deformation beyond the section to be bent and ensures the reaction to the bending stress.
The dimensional characteristics of the forming roller determine the radius of the bend thus made in the pipe, while the rotation angle of the bending arm determines the angle of the bend. However, because of the phenomenon called "backspringing," the final angle of the bend is always smaller than the set rotation angle of the bending arm.
Consequently, in order to bend a pipe to a specific angle, the rotation of the bending arm must be defined using an angle equal to said value, plus backspringing. This assumes that the backspringing value can be known or determined so that it can be taken into consideration. Of course, said backspringing can be determined theoretically, but it is also important to be able to monitor its actual value in practical applications. Such a need arises especially in adjusting an automatic bending machine before using the latter to make a series of identical bends.
A known procedure for monitoring backspringing consists of detecting the value of said backspringing on the bending machine using mechanical sensors. The implementation of this known process requires that the clamping jaws be opened, releasing the section of the pipe just bent, with the sensors coming into contact with the section of the pipe located in front of the bend formed.
The main problem with the existing process summarized above is that, after backspringing is detected, it is practically impossible to resume the bending of the pipe to reflect said backspringing in order to adjust the bend precisely to the desired angle. Indeed, the pipe needs to be clamped again between the two previously opened clamping jaws. However, the clamping of the pipe in the previous operation cannot be duplicated exactly. Thus, the clamping jaws mark the pipe, making the latter unusable. In this way, the pipe used for monitoring backspringing is wasted, which is unacceptable for pipes that are expensive because of their size and/or the material from which they are made.
Moreover, the sensors currently used to monitor backspringing constitute bulky and cumbersome supplementary devices on bending machines, located in the bending area.
East German Pat. No. DD-A-109331 teaches another process for monitoring backspringing in pipes wherein, after the bend is made, the section of the pipe located in front of said bend remains clamped, while the section of said pipe behind the bend is released, and wherein a measurement or reference mark is made on the section of said pipe located behind the bend in order to determine the backspringing value.
Thus, after bending, the pipe springs back freely, while said pipe remains fastened between the clamping jaws of the bending machine. Backspringing is detected in the released section of the pipe located behind the bend, away from the bending area. The bending can subsequently be resumed, taking the backspringing value into account, without ever interrupting the clamping of the pipe in its section located in front of the bend, and thus without marking the pipe; the pipe used to monitor backspringing is thus never wasted and consequently the principle of such a process is advantageous.
However, East German Pat. No. DD-A-109331 only proposes a device comprising a part having an angular scale mounted on the released section of the pipe and an optical sighting system mounted on the frame of the bending machine, in order to measure or identify pipe backspringing.
Such a device thus comprises a sort of external measuring instrument and its implementation requires that more parts be added to the machine and the pipe to be bent, which constitutes a first problem.
Furthermore, the actual use of such a device to measure backspringing requires two human operations, on the one hand, to perform the sighting and reading of the scale using the optical system, and, on the other hand, to set the machine for the corrective action depending on the reading obtained using the sighting system.
Thus, the use of this device requires a considerable amount of time, and the process for determining backspringing and correction according to the value of said backspringing cannot be automated.